De-Magnatizing digital callipers

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Ian Phillips on 05/07/2013 16:02:22:A coil of wire connected to an alternating supply does it all.

Agreed, and the more turns the better such as the secondary of a microwave oven transformer. I don't think anyone here has suggested using one with the primary still connected to the mains. I would hope that anyone on this forum would have more sense.

Russell.

BTW., can anyone explain the theory behind these little permanent magnet with holes demagnetisers?  I don't see how they can work.

Edited By Russell Eberhardt on 07/07/2013 11:04:26

[swarfmakerParticipant @swarfmaker]

Have a look on tinternet for a magnetic bulk eraser, it is intended for the erasing of cassette tapes, floppy discs etc. mine is about a 4in cube and it has demagnetised everything. I paid about 6 quid for it at sandown park about 3 years ago.

[Ian PParticipant @ianp]

Russell

I dont see how the permanent magnet erasers work either, it sort of defies common sense.

However I still maintain that microwave secondaries should be left out of demagnetiser considerations. A coil of wire with more turns is not automatically better, in fact too many will have higher resistance so less current and a weaker magnetic field (unless you put a higher voltage in).

The main reason to not connect the secondary to the mains is that generally only one wire of the secondary is accessible, the second wire being grounded within the transformer construction leading to a potentially dangerous situation.

Ian P

[Russell EberhardtParticipant @russelleberhardt48058]

it sort of defies common sense.

… and physics!

Russell.

[joegibParticipant @joegib]

Posted by Ian Phillips on 07/07/2013 21:11:32:

I dont see how the permanent magnet erasers work either, it sort of defies common sense.

I think the permanent magnet demagnetisers are made up of 3 bar magnets enclosed in a plastic case like so:

The magnets forming the left-hand aperture 'M' have opposite poles at each end so a magnetising field develops between them. The magnets forming the right-hand aperture 'DM' have like poles at each end so a repulsion field develops between them. So, an article passed through one or other aperture will be magnetised/de-magnetised.

They work well enough for small items like screwdrivers. Indeed, mine is more commonly used to magnetise a screwdriver — it's useful to be able to hang a screw on the end of the screwdriver when working in the depths of a computer.

Joe

[AndyfParticipant @andyf]

I must say that, had a defunct central heating pump been available, I would have followed Ian Phillip's suggestion of discarding the "wet side" and rotor and using the stator windings in the dry side, under the diaphragm which separates wet from dry. I've read that tip before.

But not having an old pump, I took the modified transformer route. At least the result is lightweight and reasonably compact .

Andy

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by joegib on 08/07/2013 14:12:24:The magnets forming the right-hand aperture 'DM' have like poles at each end so a repulsion field develops between them. So, an article passed through one or other aperture will be magnetised/de-magnetised.

I don't see how that follows. Your diagram is wrong in that between the two magnets to the right there will be a strong magnetic field running vertically between the two magnets.

Perhaps if the screwdriver gets magnetised from side to side instead of end to end it appears to be less magnetised??

I would still like to see a good explanation.

Russell.

[Russell EberhardtParticipant @russelleberhardt48058]

Here's the demagnetiser I made (lashed up) some time ago to demagnetise chuck jaws. Cost; nil. I already had the solder gun for cutting and sealing ropes and had some copper wire in the scrap box.

No high voltages and totally safe. Works fine on chuck jaws, screwdrivers and verniers.

Russell.

[joegibParticipant @joegib]

Yes, I made the mistake of theorising based on recollection of the device rather than rooting it out and examining it. I've since done that and a photo of the unit is here:

— and its innards here:

I'll not theorise further but let the assembled company pick the bones!

Joe

[Michael GilliganParticipant @michaelgilligan61133]

Joe,

Thanks for posting the pic.

From this; it looks like the "demagnetize" magnet is actually an array of magnets bonded into a block.

If the poles are suitably aligned, then the applied magnetic field would alternate as you withdraw the screwdriver.

Any chance you could check the fields ? [iron filings on a sheet of paper, or maybe use a compass] … If I'm right, the two magnet blocks will be very different.

MichaelG.

[joegibParticipant @joegib]

Hi Michael,

The striations visible in the above photo are perhaps misleading — they're slightly curved so are either grinding marks (Blanchard ground?) or sawing marks (diamond sawn?). The short sides of the blocks are smooth with no machining marks — diecast or sintered maybe? Testing with a compass indicates that the poles are located across the broad sides of each block.

Here's a diagram of the construction:

Joe

[Russell EberhardtParticipant @russelleberhardt48058]

Yes, they are sintered in a large block and sliced with a diamond saw.

I thought that was the arrangement of the magnets from your picture. That will give a magnetic field in the Magnetise slot that is zero in the centre and opposite directions at each edge. So as the screwdriver is drawn through it will be magnetised first in one direction and then in the other. You will end up with a south pole at the tip.

Now the field in the other slot will be similar but weaker so the effect will still be to magnetise the screwdriver but weaker. Perhaps if you pass it through as close as possible to the magnet and then again at the opposite side of the slot the effect will be similar to a diminishing alternating field which may reduce the residual magnetism.

I still prefer my solution.

Russell.

[jason udallParticipant @jasonudall57142]

Halbach array

[Russell EberhardtParticipant @russelleberhardt48058]

Success!

I took one magnet of a type similar to Joe's and waved it back and forth (lontitudally) over a magnetised screwdriver keeping a small gap with a piece of plastic. The result: the screwdriver was partially, but not fully, demagnetised.

Repeated the same process but gradually increasing the distance between the magnet and the screwdriver and it was de-magnetised (almost) fully.

So, the key to using these devices is to repeat the pass through at gradually increasing distance. I guess that's what the steps seen on some of them are for. Not much use for the OP's digital calipers though!

Halbach array — interesting, it might work better.

Russell.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by joegib on 09/07/2013 10:17:27:

Hi Michael,

The striations visible in the above photo are perhaps misleading — they're slightly curved so are either grinding marks (Blanchard ground?) or sawing marks (diamond sawn?). The short sides of the blocks are smooth with no machining marks — diecast or sintered maybe? Testing with a compass indicates that the poles are located across the broad sides of each block.

Joe

.

Thanks for checking, Joe

Apologies for the delay in responding; We've only just returned from a day-out.

… Looks like the mystery is solved.

MichaelG.

[I.M. OUTAHEREParticipant @i-m-outahere]

Hi all,
I picked up a degaussing wand that is used for fixing CRT in arcade machines .
Cost $16au on EBAY + a couple of bucks delivery ,I thought for that price i would give it a go !
Plugged it into the mains gave the calipers a wave over it then slowely moved them away before turning off and they are now de-magnetised .

Gave a magnetised screwdriver a go with one of those cheap magnetising/de- magnetising tools as described in this post but it would not work so i gave it a hit with the degaussing wand – instantly de magnetised , then run it thru the remagnetizing side of the magnetising tool and it was re magnetised .
Still have plans to make a bigger unit though as i don't know if this wand would be big enough to do a vise or the like .

Now i want one of those magnetic wand thingies to pick up the long curly swarf from my machines before i vacuum but they want $70 for one !
Does anyone have an idea of how to make one ?

Ian

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SLOTDRILLER on 11/07/2013 05:33:13:

Now i want one of those magnetic wand thingies to pick up the long curly swarf from my machines before i vacuum but they want $70 for one !
Does anyone have an idea of how to make one ?

Ian

.

It's constructed rather like a closed-off bicycle pump

with a button magnet where the leather washer would be.

MichaelG.

.

Edit:  Turns out that Eclipse sells one.

Edit:  and there is a thread here with a brilliant post from John S.

Edited By Michael Gilligan on 11/07/2013 07:54:17

Edited By Michael Gilligan on 11/07/2013 08:00:36

[AndyfParticipant @andyf]

Mike gave me a small one which he made, as shown here , which is very useful for picking chips off machinery. There's no reason why a much larger version couldn't be made for the floor.

Andy

[I.M. OUTAHEREParticipant @i-m-outahere]

Thanks Michael and Andy ,
Something so simple but why so expensive !
Looks like a simple project for the weekend !

Ian.

[I.M. OUTAHEREParticipant @i-m-outahere]

Just for any Australian or New Zealand residents interested in making a swarf wand as described in MEW 172 or was it 174? anyhow you can get the required magnets fron AMF MAGNETICS in Botany Australia .
No connection etc but a very east transaction over the phone and you can buy online etc .
I got 10 of 12.5 mm OD countersunk magnets rated for 12 kg pull for around $18 AU – (prices may change in the future ) you could of course buy only one magnet at around $2.50 + GST .

Not sure why a could not remember this Article in MEW ?
I suppose that at the time i was not using a Vacuum cleaner in the Workshop and dismissed it as something i would never need !
Oh how things can change in such a short time !

Ian

[Gordon WParticipant @gordonw]

I made a "swarf stick" from scrap,(except the magnet ). 3/4" copper water pipe OK 20mm, solder copper disc one end. Works great and good for finding dropped bits.

[AndyfParticipant @andyf]

On the subject of picking stuff up, I have my late mother's "reacher" – this sort of thing – in the shop, and find it very useful for recovering items which have fallen behind machines or under benches. Mine has a magnet on the end; fairly weak, but can be used to draw a small item into a better position for grabbing.

It also saves a lot of bending to pick up all the twigs my ash trees shed before I mow the lawns.

A bit off topic, but we seem to have picked the bones out of demagnetisers.

Andy

[Ian S CParticipant @iansc]

For magnets in NZ , Magnets New Zealand Ltd. brett@magnets.co.nz

Web site http://www.magnets.co.nz

I have had good service from this place. I made my fist order to the company, and just as I sent the E-mail, a TV program came on about the amazing stuff they are making in the magnetic equipment line in their Auckland factory. Ian S C

[Clive HartlandParticipant @clivehartland94829]

A swarf picker up device is simply a magnet in a plastic bag and then cart the swarf to the bin and remove the magnet from the plastic bag!

Simples.

Clive

[I.M. OUTAHEREParticipant @i-m-outahere]

I had a play around in the workshop today and one job was to mill some keyway slots on the mill , i chose the x2 as they were only 4mm and it has a higher speed capabillity than the HM46.
I had recently purchased a screwless vise off ebay and it was cheap but acceptable for what i want to do but when i sat a parrallel on the vice it immediately stuck to the fixed jaw , so the vise was magnetic or at least this jaw was .
Out with the degaussing wand i purchased to give it a go and i was not expecting a result as it was still clamped to the table but i had to give it a go.
I had to try without removing the vise as i had only trammed it a few days earlier so i had nothing to lose .
After 3 passes with this cheapo wand it was de magnetised and i couldn't believe my luck !

Thanks Ian sc for the links as it gives us southern hemispherians  an option or two !
 

Ian

Edited By SLOTDRILLER on 13/07/2013 11:38:31

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